Engine hood comprising a protective device for pedestrians

ABSTRACT

An engine hood for motor vehicles has a deformable head impact zone to protect pedestrians in the event of a collision with the motor vehicle. The engine hood comprises an outer shell, which is formed by the body paneling, and an inner shell which is arranged below the outer shell and is connected to the outer shell. The inner shell is provided with a vault-structured stiffening region in the region of the head impact zone.

BACKGROUND

The invention is based on an engine hood for motor vehicles, which isprovided with a deformable head impact zone to protect pedestrians inthe event of a collision with the motor vehicle, as is known, forexample, from EP 1 093 980 A1.

In the event of a pedestrian colliding with a vehicle, in particular inthe event of a head-on impact, the upper body or head of the pedestrianoften strikes the engine hood of the vehicle, which can cause seriousinjury to the pedestrian. To reduce this risk of injury, the region ofpotential impact of the pedestrian on the engine hood has to be asyielding and deformable as possible. However, there is only a very smallamount of free space available between the engine hood and the equipmentbelow it, and consequently the deformation movement by which the enginehood can yield in the event of a collision with a pedestrian is onlyvery small. Furthermore, to protect the occupants of the vehicle in theevent of a head-on collision, the engine hood has to satisfyrequirements relating to component rigidity and has to be configured insuch a way that defined deformation and therefore a controlledconversion of energy occur in the event of the engine hood crumpling inthe longitudinal direction of the vehicle.

To satisfy these contradictory demands, the engine hood is in many casesconfigured as an assembly of an outer shell (which forms the bodypaneling) and a reinforcing shell, which is arranged below the outershell and is provided with suitable deformation and stiffening elements.The generic EP 1 093 980 A1 has disclosed, for example, an engine hoodwith an outer shell and a reinforcing shell, the flexural rigidity ofwhich varies over the engine hood in such a way that the engine hood hasa relatively high flexural rigidity in the center but a lower flexuralrigidity in the edge regions. This design is intended to ensure that inthe event of a central head impact, the entire mass of the engine hoodcounteracts the impact, whereas in the event of a head impact in theedge regions, the energy of the head impact is dissipated over a smallpart of the engine hood. The design of the engine hood which is knownfrom EP 1 093 980 A1 therefore aims to achieve an approximately constantdeformation of the engine hood irrespective of the impact site.

However, current knowledge has shown that when assessing the effects ofa collision of a pedestrian with the engine hood, it is not only thebending of the engine hood but also, to a much greater extent, theacceleration or deceleration of the impacting body, i.e. the forcesacting on the body, which play an important role. In addition, asbefore, the maximum possible free space has to be available betweenengine hood and the equipment below it, so that in the event of acollision with a pedestrian, the engine hood can yield by the largestpossible deformation movement before it comes into contact with the(generally very hard) equipment below it.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an the engine hood thatprovides a substantially homogeneous force level over the engine hood inthe event of pedestrians colliding with the vehicle. A further oralternate object of the invention—given a predetermined form of theengine block and the outer paneling—is to provide a substantially largedeformation movement by which the engine hood can yield in the event ofa pedestrian colliding with the vehicle without hitting the engineblock.

The present invention provides an engine hood for motor vehicles whichhas a deformable head impact zone to protect pedestrians in the event ofa collision with the motor vehicle. The engine hood includes an outershell, which is formed by the body paneling, and at least one innershell, which is arranged below the outer shell and is connected to theouter shell, characterized in that the inner shell has a stiffeningregion which is provided with a vaulted structure. The vaulted structureis being formed by local folding with only an insignificant increase inthe surface area of the material.

Accordingly, the engine hood is configured as a composite part made upof an inner shell and an outer shell, the inner shell being providedwith a stiffening region which has a vaulted structuring. A“vault-structured” component region in this context is to be understoodas meaning a component region which has been provided with a stiffeningmacrostructure which has been introduced into the semi-finished productused to produce the component with the aid of a bulging process. Theprocess used to produce bulge-structured semi-finished products of thistype is described, for example, in DE 44 37 986 A1.

Unlike when using conventional deformation processes (such as forexample embossing or hydroforming), in which the starting material isplasticized during forming, in the case of vault-structuring thesemi-finished product is merely folded locally; this process isassociated with only an insignificant increase in the surface area ofthe material. The bulge-forming is effected in a continuous process, sothat entire webs of material (or band-like regions on them) are providedwith the vaulted structure.

To produce the inner shell of the engine hood, a blank is cut out of thevault-structured web of material and is then shaped into the inner shellby further process steps. Alternatively, an insert part, the size andshape of which are matched to the stiffening region of the inner shell,can be cut out of the vault-structured semi-finished product; in afurther process step, this insert part is fitted into a cutout providedfor this purpose in the inner shell, which is formed conventionally(e.g. by deep-drawing) from an unstructured metal sheet, and connectedto the inner shell.

The vault-structuring is associated with a considerable increase in therigidity of the associated semi-finished product and the componentproduced therefrom. Unlike in the procedure which is known (for examplefrom EP 1 093 980 A1) of providing the inner shell with beads whichincrease the rigidity, vault-structuring has the advantage of effectingan increase in rigidity which is substantially direction-independent.Therefore, a vault-structured stiffening region of the inner shell,which spans the majority of the impact region, can achieve a virtuallydirection-independent, constant rigidity and mass distribution of theinner shell in the impact region. This ensures a homogeneous force levelor energy absorption capacity over the whole of the vault-structuredregion of the engine hood.

In the event of a crash, vault-structured components are distinguishedby a high energy absorption and a regular, reproducible deformation.This plays an important role in protecting the vehicle occupants in theevent of a head-on collision, since the inventive configuration of theinner shell with vault-structured deformation region allows well-definedcrumpling of the engine hood in the longitudinal direction of thevehicle and therefore a controlled conversion of energy.

A further advantage of the invention consists in the fact that thebulges which are introduced into a web of material during thevault-structuring have a very low height compared to the beads which arestamped in in the conventional way. The result of this is that theeffective component thickness of the vault-structured stiffening regionof the engine hood inner shell is significantly lower than the effectivecomponent thickness of conventional beaded inner shells. This saving onthe effective component thickness means that the inner shell accordingto the invention takes up significantly less space than conventionalinner shells, so that a larger free space remains between the engineblock and the paneling (outer shell) of the engine hood; this free spacecan be used as deformation movement for the engine hood in the event ofa pedestrian colliding with the vehicle.

To summarize, the configuration of the engine hood according to theinvention with an inner shell which is vault-structured in regionstherefore produces significant advantages over a conventional beadedinner shell, namely:

-   -   a very homogeneous force level and therefore a very homogeneous        energy absorption capacity in the vault-structured region of the        engine hood, and    -   a low effective thickness of the inner shell in the region of        the engine block and therefore a greater free deformation        movement of the engine hood in the event of a collision.

The vault-structured stiffening region expediently spans the whole ofthe central region of the inner shell which is located above theequipment in the engine compartment in the vehicle over a large surfacearea. Along the side regions and in the front region, where additionalreinforcements to the inner shell have to be provided for the hinges orbrackets, the inner shell has, instead of the (direction-independent)vaulted structuring, a targeted stiffening structure which is matched tothe mating brackets on the body and is reinforced by additionalelements.

According to an advantageous configuration of the invention, thestiffening region of the inner shell is formed by an approximatelyplanar vault-structured insert part, which is produced separately from avault-structured semi-finished product and during bodyshell assembly isfitted into a cutout in the inner shell (which has been produced, forexample, by deep-drawing) and fixedly connected to the latter. Thisstructure of the inner shell is particularly expedient with regard todeformation technology aspects, since the vault-structured insert partcan be manufactured separately and only a small amount of smoothing ordeformation of the vaulted structure is required.

To allow easy attaching of the insert part to the inner shell with theaid of conventional, tried-and-tested processes which are suitable forlarge-scale series production—e.g. by spot welding and/or adhesivebonding—and thereby to enable a high-strength join to be ensured in areliable way, the vaulted structure is advantageously smoothed in theedge region of the insert part. This produces a smoothed flange at theedge of the insert part, which in the position in which the insert partis to be assembled with the inner shell comes to bear against acorrespondingly shaped flange on the inner shell and is connected to thelatter by a joining process, preferably by adhesive bonding. Thesmoothing of the edge regions of the insert part is carried out in aparticularly cost-effective way with the aid of a stamping process.

The vault-structuring of the stiffening region on the inner shell isadvantageously oriented in such a way that the bulges are vaultedupward, i.e. toward the outer shell. To achieve a particularlyhomogeneous rigidity and strength of the engine hood in the impactregion, the upwardly protruding domes of the bulges are expedientlyadhesively bonded to the outer shell.

BRIEF DESCRIPTION OF THE DRAWINGS

The following text provides a more detailed explanation of the inventionon the basis of an exemplary embodiment illustrated in the drawings, inwhich:

FIG. 1 shows an exploded view of an engine hood according to theinvention;

FIG. 2 shows an exploded view of the inner shell of the engine hoodshown in FIG. 1;

FIG. 3 shows a diagrammatic sectional illustration through an assemblyof outer shell and inner shell, in accordance with section III-III inFIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows an exploded illustration of an engine hood 1 with an outershell 2 which has been reinforced by an inner shell 3. In the presentexample, both shells 2, 3 consist of sheet metal; however, they may ingeneral also be made partly or completely from other materials, inparticular from fiber-reinforced plastics.

The outer shell 2 is a deep-drawn metal sheet which is connected to theinner shell 3 as part of the bodyshell assembly. The inner shell 3 is acomposite component and comprises—as can be seen from the explodedillustration presented in FIG. 2—a base part 4, which is reinforced inthe bracket regions 5 by additional metal reinforcing sheets, namely thehinge reinforcements 6 and the front metal stiffening sheet 7. The basepart 4 and the reinforcing parts 6, 7 are typically deep-drawn partsformed from sheet metal (steel, aluminum). In the bracket regions 5 andthe edge regions 8, the base part 4 is stiffened by beads 9.Furthermore, a stiffening region 10, which covers the majority of theengine compartment 25 located below the engine hood 1 in the vehicle, isprovided in the interior of the inner shell 3. In this stiffening region10, the base part 4 has a cutout 10′, into which an insert part 11 issecured using an adhesive bonding process. The macro-geometry of theinsert part 11 is—as can be seen from FIGS. 1 and 2—approximatelyplanar, allowing a flat shape of the engine hood 1 to be achieved.

The insert part 11 is produced from a vault-structured blank of sheetmetal. The vaulted structure 12 on the blank is produced with the aid ofa bulging process, which is described in detail, for example, in DE 4437 986 A1; this bulging process produces a vault-structured insert partblank from a planar metal starting sheet. Since the vaulted structure 12is introduced in a continuous process, the insert part blank has thevaulted structuring 12 over its entire surface. Alternatively, thestarting material used for production of the insert part 11 may also bea blank which—instead of being fully vault-structured—is provided with avaulted structuring only in a central band-like strip (corresponding tothe direction of advance of the bulging process), whereas the adjacentedge strips are devoid of vaulted structures.

The vaulted structure 12 of the insert part 11 in the present exemplaryembodiment has a hexagonal symmetry, which is diagrammatically indicatedin FIG. 1 by a honeycomb pattern. The grid or lattice constant 13 andthe vault height 14 of the vaulted structure 12 are in this case matchedto the material thickness and the desired increase in rigidity of theinsert part 11. The optimum shape and orientation of the vaultedstructure 12 on the insert part 11 is advantageously determined innumerical strength tests and crash simulations carried out on the enginehood 1. As an alternative to the hexagonal vaulted structure 12 shown,the insert part 11 may also have a vaulted structure with a triangularor rectangular basic symmetry. Since the vaulted structure 12 of theinsert part 11 is highly symmetrical (in the form of a regular hexagonalgrid in the case of FIGS. 1 and 2), this vaulted structure 12 has anapproximately direction-independent stiffening effect on the insert part11. Therefore, a constant, predetermined force loading or decelerationin the event of a test body striking the engine hood 1 can be achievedin different test zones in the area of the impact region 15 which iscovered by the insert part 11 (and indicated by dashed lines in FIG. 1).At the same time, the engine hood 1 has a homogeneous area moment ofinertia over the impact region 15.

Along its edge 16, the insert part 11 is provided with connection zones17, which are substantially devoid of vaulted structures 12 and are inthe form of flat flanges. In these connection zones 17, the vaultedstructure 12 which was originally present on the insert part blank hasbeen smoothed by a stamping process. The connection zones 17 areconfigured in such a way that the insert part 11 can be attached to thebase part 4 with the aid of conventional joining processes (preferablyby adhesive bonding, or alternatively, by way of example, byspot-welding); the base part 4 is likewise approximately flat in theregion of overlap with the connection zones 17.

Beads (not shown in FIGS. 1 and 2) may be provided on the insert part 11in a transition region 19 between connection zones 17 and vaultedstructure 12; these beads serve to “consume” the excess material whichhas been formed as a result of the increase in surface area during thevault-structuring and now has to be removed in a controlled way duringsmoothing of the connection zones 17 of the insert part 11. The beadsare dimensioned and arranged in such a way that on the one hand theyprevent creases from forming in the smoothed connection zone 17 and onthe other hand prevent smooth material from being pushed into thevaulted structure 12 of the insert part 11.

After the reinforcing parts 6, 7 and the insert part 11 have been joinedto the base part 4, the inner shell 3 produced in this way is joined tothe outer shell 2 to form the engine hood 1. To securely join thevault-structured insert part 11 to the outer shell 2, the upwardlyprojecting bulge domes 20 of the vaulted structure 12 of the insert part11 are adhesively bonded to the opposite inner side 21 of the outershell 2. As can be seen from FIG. 3, a sheet-metal composite, theeffective thickness 22 of which is determined by the sheet-metalthicknesses of the outer shell 2 and of the insert part 11 and by thevault height 14 of the vaulted structure 12, is then formed in theregion of the insert part 11. Since the vaulted structuring has a verylow vault height 14—compared to a beaded arrangement which iscustomarily used—the effective thickness 22 of the engine hood 1 is alsosignificantly lower in this impact region 15 than in the case of theconventional engine hoods which are stiffened by beads: for example, inthe case of metal sheets which are between 0.7 mm and 1.2 mm thick, asare typically used for the inner shell 3, the bulges, for honeycombsizes of 25-50 mm, protrude only approximately 2-4 mm out of the web ofmaterial. The result of this is that the effective clear height 23 whichis left between the inner side 24 of the engine hood 1 and the equipment25 of the engine block (which is indicated by dashed lines in FIG. 3) issignificantly greater throughout than if a conventional beaded enginehood is used. This increase in clear height 23 leads to an increase inthe deformation movement which the engine hood 1 has to cover in theevent of a collision with a pedestrian before the engine hood 1 strikesthe equipment 25. Consequently, the engine hood 1 according to theinvention, with an inner shell 3 which has been vault-structured inregions, on the one hand offers a particularly homogeneous force loadingover the impact region 15, and on the other hand—given a predeterminedarrangement of the engine compartment equipment 25 and the outer skin 2of the engine hood 1—allows a particularly large free deformationmovement 23. Therefore, the pedestrian can be better protected in theevent of impact on the vehicle by the configuration of the engine hood 1according to the invention.

In addition to the configuration of the inner shell 3 described above asan assembly of a deep-drawn base part 4 and a vault-structured insertpart 11, the inner shell 3 may also be produced entirely from avault-structured blank, which has been suitably smoothed and providedwith strength-increasing beads 9 in the region of the bracket regions 5and of the edges 8 (using a deep-drawing process). Although thisconfiguration of the inner shell 3 eliminates the process step ofadhesively bonding the (separately produced) insert part in place, thelarge-area smoothing and deformation of a vault-structured metalsheet—as described for example in patent application 102 1512.2-14—imposes high demands on the configuration of the drawing tool,and consequently the production of the inner shell as a single-partcomponent from a vault-structured metal sheet is associated withincreased outlay on deep-drawing equipment.

1. An engine hood for a motor vehicle having a deformable head impactzone to protect pedestrians in the event of a collision with the motorvehicle, the engine hood comprising: an outer shell formed by a panelingof a body of the vehicle; at least one inner shell disposed below theouter shell and connected to the outer shell, the inner shell having astiffening region, wherein the stiffening region includes a vaultedstructure including a grid of bulges formed by local folding of amaterial of the inner shell so as to insignificantly increase thesurface area of the material.
 2. The engine hood as recited in claim 1,wherein the inner shell includes a base part defining a cutout and aninsert part disposed in the cutout and fixedly connected to the basepart, and wherein the stiffening region is formed by the insert part. 3.The engine hood as recited in claim 2, wherein the insert part includesa semi-finished product having a smooth edge region and avault-structured portion.
 4. The engine hood as recited in claim 2,wherein the insert part includes an edge region and is adhesively bondedto the base part at the edge region.
 5. The engine hood as recited inclaim 1, wherein the vaulted structure defines a plurality of bulgedomes vaulted out in a direction toward the outer shell.
 6. The enginehood as recited in claim 5, wherein the plurality of bulge domes of thevaulted structure are adhesively bonded to the outer shell.
 7. Theengine hood as recited in claim 1 wherein the inner shell is between 0.7mm and 1.2 mm thick.
 8. The engine hood as recited in claim 1 whereinthe bulges protrude more than 2 mm.
 9. The engine hood as recited inclaim 1 the vaulted structure includes a honeycomb structure withhoneycomb sizes of 25 to 50 mm.
 10. The engine hood as recited in claim1 wherein the vaulted structure includes hexagonal structures.
 11. Theengine hood as recited in claim 1 wherein the vaulted structure includestriangular or rectangular structures.
 12. The engine hood as recited inclaim 1 wherein the vaulted structure includes bulges protruding lessthan 4 mm.
 13. An engine hood for a motor vehicle having a deformablehead impact zone to protect pedestrians in the event of a collision withthe motor vehicle, the engine hood comprising: an outer shell formed bya paneling of a body of the vehicle; at least one inner shell disposedbelow the outer shell and connected to the outer shell, the inner shellhaving a stiffening region, wherein the stiffening region includes avaulted structure including local folding of a material of the innershell so as to insignificantly increase the surface area of thematerial, the vaulted structure having a grid or lattice constant andvault height matched to a material thickness and desired rigidity of theinner shell.
 14. A method for manufacturing the engine hood as recitedin claim 1 comprising: creating the vaulted structure in a continuousweb process.